Apparatus for amplifying electrical energy



Mal-id! 1931. E R. A. BIERWIRTH 1,795,194

APPARATUS FOR AMPLIFYING ELECTRICAL ENERGY Filed July 12. 1927 (III -lOOI000 IOOOO Fesousucy i/v Cyc/zs pm SECOND.

Inventor;

. Rudolph A-B i er-wirth,

His Attorney Patented Mar. 3, i931 Wires stares caries T RUDOLPH A. BIEBWIRTH, F SCHEIIECTADY, YGRK, ASSIGNOE- TO GENERAL ELEC- TRIC comrartnnGGEEGRATIGN OF NEW YORK APPARATUS FOR AMILIEYZNG ELECTRICAL ENERGYApplication filed July 12,

My invention relates to apparatus for amplifying electrical energy, suchas that util ized in communication systems and the like, and has for itsprincipal object the provision of an improved apparatus and method ofoperation which may be utilized over a wide range of audio frequencieswithout substantial change in the ratio of amplification.

In the operation of the transformer or impedance coupled amplifierheretofore provided, difficulty has been encountered due to the factthat the amplification ratio varies. with frequency. In accordance withmy invention, this difiiculty is avoided by the use of a couplingelement whereina capacity and a plurality of inductances are so relatedto the other elements of the amplifier as to produce a substantiallyconstant transformation ratio over afrequency range which ineludes lowaudio frequencies. I

My invention will' be better understood from the following descriptionwhen considered in connection with the accompanying drawing and itsscope will be pointedout in the appended claims.

Referring to the drawings, Fig. 1 shows an amplifying apparatus whereinmy invention has been'embodied; and Fig. 2 relates to the operation ofthe apparatus shown by Fig. 1. Y

changing its transformation ratio.

1927. SerialNo. 205,203.

cuit being connected through the condenser 8 to the plate circuit of thedevice 4 and its secondary circuit being included in the grid circuit ofthe device 5. It will be apparent that the winding 7 may be replaced bya transa" former provided with separate-primary and secondary circuitsand that its intermediate terminal may be ad]usted for the purpose of rIn order that the amplification ratio may be maintained substantiallyconstant over a wide range of frequencies, it is necessary that theincluctances L and L of the windings 6 and 7 and the capacity C of thecondenser 8 bear a certain definite relation to the anode or platecircuit resistance R of thedevicet and the primary circuit resistance Rof the This apparatus comprises input terminals 1 and output terminals 2which are interconnected through means comprising a transformer 3, spacedischarge devices 4L and 5, o and'a coupling element consisting ofwind-. ings 6 and 7 and a condenser 8 connected between one terminal ofthe winding 6 and a terminal intermediate theends of the winding '2which may function as an auto-transformer. I

Resonance occurs when the term of the rlght hand bracket is zero. Underthese conditions If L7 andzcs'al'e given the Pr per valties, the ratiothe auto-translowest frequency which it is desired to amplify uniformlyand this frequency is assumed to be f the ratio Substituting the valueof C from Equation (2) This equation indicates that there are aninfinite number of combinations of L and L which will make at w e) and Cequal to the expression in Equation (2) it follows that ei-er 'CombiningEquation with Equation i) and neglecting small quantities, 1t fol- For m=2w these equations give the following:

The relation between the resistance of the device 4, which may be anydevice having resistance without appreciable inductance the inductance6; the capacity 8, and the resistance and reaetance of the primarycircuit H 1 1 1 may be expressed as follows. The internal resistance ofthe device 4 plus the resistance of the primary circuit of thetransformer 7 is made substantially equal to each of the reactance ofthe capacity 8, to the reactance of the primary circuit of transformer7, and to one half the reactance of the inductance 6 at the lowestfrequency in the range of frequencies which it is desired to amplifysubstantially uniformly.

Taking R; as 12000 ohms R- as 1000 ohms, f as 30 cycles, L as 150lienries, L as 70 henries, and C as A15 microfarads, the followingvalues of E AMEM are found for different values of frequency:

E (in percent of transformaf AME tion ratio) Fig. 2 shows the resultsdetermined experimentally with L henries, L 37 henries,

tl =l microfarad, f =27 cycles, R =5100, and a 1 to 4r transformerratio. It will be observed that between 30 and 7000 cycles there is avariation in the ratio 05 AME of only about three percent. This showsthat the amplification ratio of the apparatus is substantially constantthroughout the entire audio frequency range.

It will be noted that the calculated Values are slightly higher than theexperimentally determined values at the low frequency end of the curve.This difference is due to the core loss which was not taken intoconsideration in the calculation. In the apparatus used to secure thedata on which the curve is based, the flux density was comparativelyhigh for an interstage transformer. is kept low, the core less effect ispractically negligible and the conditions under which substantiallyconstant transformation ratio over a wide range of frequencies ispossible can be readily determined from equations (8), (9) and (10).

The embodiment of the invention illustrated and described herein hasbeen selected for the purpose of clearly setting forth the 3-:1

principles involved. It will be apparent, however, that the invention issusceptible of being modified to meet the diiferent conditionsencountered in its use andI therefore aim to cover by the appendedclaims all mod- If the flux density T if ifications within the truespirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. In an audio frequency amplifier, the combination of a space dischargedeviCeprovided with an anode circuit, an inductance connected insaid'circuit, a capacity, and a transformer provided with a primarycircuit connected to said anode circuit through said capacity, theinternal resistance of the space discharge device plus the resistance ofthe primary circuit of the transformer being substantially equal to eachof the reactance of the capacity, to the reactance of the primarycircuit, and to one half the reactance of the inductance at the lowestfrequency in the range of audio frequencies which it is desired toamplify substantially uniformly. p

2. In an audio frequency amplifier, the combination of a pair of spacedischarge devices each provided with an input and an output circuit, aninductance connected in theoutput circuit of one of said devices, acapacity, and a transformer provided with a primary circuit connected tosaid output circuit through said capacity and with a secondary circuitconnected in the input circuit of the other of said devices, theinternal resistance of said one of said devices plus that.

of said primary circuit being substantially equal to the reactance ofsaid capacity, to each of the reactance of said primary circuit, and toone half the reactance of the inductance at the lowest frequency in therange of audio frequencies whichit is desired to amplify substantiallyuniformly.

3. An audio frequency amplifying apparatus including a space dischargedevice provided with an anode circuit, an inductance connectedin saidanode circuit, a capacity, and a transformer provided with a primarycircuit connected to said anode circuit through said capacity, themagnitudeof said" inductance in henries being substantially equal to.373 times the resistance of said anode circuit in ohms divided by thelowest audio frequency in cycles per second which it is desired toamplify.

4. An audio. frequency amplifying apparatus including a space dischargedevice provided with an anode circuit, an inductance connected in saidanode circuit, a capacity,. r and a transformer provided with a prlmarycircuit connected to said anode circuit through said capacity, theinductance of said primary circuit in henries being substantially equalto the lowest audio frequency in cycles per second that it is desired toamplify di- 1 vided into the sum of 159 times the res1st-= ance of saidanode circuit in ohms and .188 times the resistance of said primarycircuit in ohms. i

5. An audio frequencyiamplifying apparatus including aspace dischargedevice provided with an anodecircuit, an inductance connected in saidanode circuit, a capacity, and a transformer provided with aprlmarycircuit connected to 'said anode circuit m through said capacity,the magnitude of said capacity in microfarads being substantially equalto the quotient obtained by dividing .159 by the product of the lowestaudio frequency in cycles per second which it is de sired to amplify andthe sum of the resistance of said anode circuit 111 ohms and .75 timesthe resistance" of said primary circuit in vice in ohms'and inverselyproportional to the lowest frequency which it is desired to transmitthrough said element. 7

7. In an audio frequency amplifier, a device for the transmission ofaudio frequency currents having a certain internal resistance, an outputcircuit therefor, a capacity, and an audiofrequency transformer having aprimary circuit connected with said output circuit through saidcapacity, the reactances of said capacity and of said primary circuit atthe lowest frequency in the range of audio frequencies which it isdesired to amplify substantially uniformly being substantially:

equal to each other and to the internal resistance of said device plusthat of the primary circuit. I

8. In an audio frequency amplifier, a dev ce for the transmlssion ofaudio frequency currents having a certain internal resistance,

an output circuit therefor, a capacity,an-

audio frequency transformer having a pri- 'mary circuit connected withsaid output circuit through said capacity, the reactances of saidcapacity and of said primary circuit at ance of said device plus that ofthe primary circuit, and'means for supplying currentto said outputcircuit including an impedance having a reactance at said lowest audiofrequency greater than that of said primary clrcuit.

9. An audio frequency amplifying apparatus including a space dischargedevice provided with an anode circuit, an inductance connected in saidanode circuit, a capacity, and a transformer provided with a primarycircuit connected to said anode circuit through said capacity, themagnitude of said inductance in henries being substantially equal to.373 times the resistance of said anode circuit in ohms divided by thelowest audio frequency in cycles per second Which it is desired toamplify, the inductance of said primary circuit in henries beingsubstantially equal to the lowest audio frequency in cycles per secondthat it is desired to amplify divided into the sum of .159 times theresistance of said anode circuit in ohms and .188

times the resistance of said primary circuit in ohms, and the magnitudeof said capacity in microfarads being substantially equal to thequotient obtained by dlvlding .159 loy the product of the lowest audiofrequency in cycles per second which it is desired to amplify and thesum of the resistance of said anode circuit in ohms and .75 times theresistance of said primary circuit in ohms.

In Witness Wl1I-'60f,-I have hereunto set my hand this 11th day of July,1927.

RUDOLPH A. B'IERWIRTH'.

- Certificate of Correction Patent No.1,795,194. g Granted March 3,1931, to RUDOLPH A. BIERWIRTH It is hereby certified that error appearsin the printed specification of the abovenumbered patent requiringcorrection as follows: Page 2, line 30, for u =w read co =w same page atthe beginning of equation 7 between lines 45 and 50, for L m read L =iand that the said Letters Patent should be read with thesecorrectionstherein that the same may conform to the re cord of thecasein the Patent Oflice.

Signed and sealed this 31st day of March, A. D. 1931.

[SEAL] M. J. MOORE,

Acting Commissioner of Patents.

